Conventionally, an ignition plug has been used in an internal combustion engine. An ignition plug has a ground electrode that forms a gap. As a ground electrode, an electrode having a ground electrode base material, and a ground electrode tip formed of noble metal that is fixed to the ground electrode base material has been used. For example, Japanese Patent Application Laid-Open (kokai) No. S62-268079 discloses a technique of providing a front end portion of a ground electrode base material with a hole for tip fixation, and disposing a ground electrode tip in the hole for tip fixation. In this technique, the ground electrode tip is fixed to the ground electrode base material by disposing a fixing member on the side opposite to the discharge surface of the ground electrode tip in the hole for tip fixation, and fixing the fixing member to the ground electrode base material.
However, it cannot be said that a sufficient device has been made, in the above-described technique, for the detailed structure for fixation of the fixing member to the ground electrode base material. Therefore, it has been impossible to fix the fixing member to the ground electrode base material with a sufficient strength, and there has been a possibility that the ground electrode tip falls off from the ground electrode base material.
The present specification discloses a technique of preventing a ground electrode tip from falling off from a ground electrode base material by improving the strength with which a fixing member is fixed to the ground electrode base material, in an ignition plug including the fixing member that fixes the ground electrode tip to the ground electrode base material.